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MECHANICAL INTESTINAL OBSTRUCTION (NEONATAL INTESTINAL OBSTRUCTION…
MECHANICAL INTESTINAL OBSTRUCTION
MECHANICAL OBSTRUCTION
CLASSIFICATION
intestinal obstruction is a restriction to the normal passage of intestinal contents. it may be divided into 2 main groups: paralytic and mechanical
mechanical intestinal obstruction is further classified according to the following:
site: high or low
synonymous with small or large bowel obstruction
nature: simple versus strangulating
simple occurs when the bowel is occluded without damage to its blood supply
strangulating - when the blood supply of the involved segment is cut off (As may occur, eg in strangulated hernia, volvulus, intussusception or when a loop of intestine is occluded by a band).
gangrene of the strangulated bowel is inevitable if left untreated
speed of onset: acute, chronic, acute on chronic
in acute obstruction, the onset is rapid and the symptoms seere
in chronic obstruction, the symptoms are insidious and slowly progressive (as for eg in most cases of carcinoma of the large bowel)
a chronic obstruction may develop acute symptoms as the obstruction suddenly becomes complete, eg when a narrowed lumen becomes totally occluded by inspissated bowel contents - this is termed acute-on-chronic obstruction
aetiology
whenever one considers obstruction of a tube anywhere in the body, the causes should be classified into the following:
causes in the wall
congenital atresia, Crohn's disease, tumours, diverticulitis of the colon, carcinoma of the colon
causes outside the wall
strangulated hernia (external or internal), volvulus and onstruction due to adhesions or bands
causes in the lumen
faecal impaction, gallstone 'ileus', food bolus, parasites (Eg ascaris worms in small bowel), intussusception
also useful to think of common intestinal obstructions that may occur in each age group
infants - intussusception, Hirschsprung's disease, strangulated hernia and obstruction due to Meckel's diverticulum
the elderly: strangulated hernia, carcinoma of the colon, colonic diverticulitis, impacted faeces
neonatal - congenital atresia and stenosis (eg duodenal atresia), imperforate anus, volvulus neonaroeum, hirschprung's disease and meconium ileus
young adults and middle age: strangulated hernia, adhesions and bands, Crohn's disease
a strangulated hernia is an important cause of intestinal obstruction from infancy to old age. the hernial orifices must therefore be carefully examined in every case.
PATHOLOGY
when the bowel is obstructed by a simple occlusion, the intestine distal to the obstruction rapidly empties and becomes collapsed
the bowel above the obstruction becomes dilated, partly with gas (most of which is swallowed air) and partly with fluid poured out by the intestinal wall together with the gastric, biliary and pancreatic secretions
there is inc peristalsis in an attempt to overcome the obstruction => intestinal colic
as bowel distends - blood supply to the tensely distended intestinal wall becomes impaired and in extreme cases, there may be mucosal ulceration and eventually perforation
perforation may also occur from the pressure of a band or the edge of the hernia neck on the bowel wall, producing local ischaemic necrosis, or from pressure from within the gut lumen, eg by a faecal mass (stercoral ulceration)
in strangulating obstruction, the integrity of the mucosal barrier is lost as ischaemia progresses, so bacteria and their toxins can no longer be contained within the lumen
transudation of organisms into the peritoneal cavity rapidly takes place, with secondary peritonitis.
unrelieved strangulation is followed by gangrene of the ischaemic bowel with perforation
the lethal effects of intestinal obstruction result from fluid and electrolyte depletion owing to the copious vomiting and loss into the bowel lumen, protein loss into the gut and toxaemia due to migration of toxins and intestinal bacteria into the peritoneal cavity, either through the intact but ischaemic bowel wall or through a perforation
CLINICAL FEATURES
4 cardinal symptoms of intestinal obstruction are:
distension
this is particularly marked in chronic large bowel obstruction and also in volvulus of the sigmoid colon
in a high intestinal obstruction, there may only be a short segment of bowel proximal to the obstruction, and distension will not then be marked
absolute constipation
failure to pass either flatus or faeces.
although it is a usual feature of acute obstruction, a partial or chronic obstruction may be accompanied by the passage of small amounts of flatus
absolute constipation is an early feature of small bowel obstruction as, even when the obstruction is complete, the patient may pass one or two normal stools as the lower bowel empties after the onset of the obstruction
colicky abdominal pain
usually the first symptoms of intestinal obstruction.
in small bowel obstruction, it is perimubilical; in distal colonic obstruction, it may be more suprapubic in location
in postoperative obstruction, the colic may be disguised by the general discomfort of the operation and by opiates that the patient may be receiving
vomiting
usually occurs early in high obstruction, but is often late or even entirely absent in chronic or in low (large bowel) obstruction.
in the late stages of intestinal obstruction, the vomiting becomes faeculent but not faecal
the faeculent vomiting is due to bacterial decompensation of the stagnant contents of the obstructed small intestine and of the altered blood that may transude into the bowel lumen
true vomiting of faeces only occurs in pts with gastrocolic fistula (eg because of a carcinoma of the stomach, carcinoma of the colon or ulceration of a stomal ulcer into the colon), or in coprophagists
it is important to note that not all of these 4 features need necessarily be present in a case of intestinal obstruction. the sequence of onset of symptoms will help localise the obstruction to the upper or lower intestine
CLINICAL EXAMINATION
a raised temp and a tachycardia suggest strangulation
the abdo is distended and visible peristalsis may be present
the pulse is usually elevated but the temp is frequently normal
visible peristalsis itself is not diagnostic of intestinal obstruction, as it may be seen in the normal subject if the abdo wall is very thin
he or she is in pain and may be rolling about with colic
during inspection it is important to look carefully for 2 feature:
1) the presence of a strangulated external hernia, which may require a careful search in the case of a small strangulated femoral hernia in a very obese and distended pt
2) the presence of an abdominal scar. intestinal obstruction in the presence of this evidence of a prev operation immediately suggests adhesions or a band as the cause
The pt may be obviously dehydrated if vomiting has been copious [abundant]
palpation reveals generalised abdominal tenderness.
a mass may be present (eg in intussusception or carcinoma of the bowel)
bowel sounds accentuated and tinkling
rectal exam must never be omitted - may reveal obstructing mass in pouch of douglas, apex of an intussusception or faecal impaction
SIMPLE VS STRANGULATING OBSTRUCTION
features suggesting strangulation include:
tenderness and abdo rigidity more marked
bowel sounds becoming reduced or absent, reflecting peritonism
colicky pain, becoming continuous as peritonitis develops
raised WCC mostly neutrophils which is usual with infarcted bowel
toxic appearance, with a rapid pulse and some elevation of temperature
SPECIAL IX
CT with oral water-soluble contrast eg GASTROGRAFIN - can localise site of obstruction detect obstructing lesions and colonic tumours and may diagnose unusual hernias eg obturator hernias
water soluble contrast study - an emergency contrast enema may detect a suspected large bowel obstruction due to carcinoma or diverticular disease
unlike a normal barium enema, no pre-exam laxative is given because of the risk of exacerbating the obstruction and causing perforation if a closed loop exists
abdo x rays (Erect and supine) - a loop or loops of distended bowel are usually seen, together with fluid levels on an erect film
small bowel obstruction is suggested by a ladder pattern of dilated loops , their central position and by striations that pass completely across the width of the distended loop produced by the circular mucosal folds
distended large bowel tends to lie peripherally and to show the haustrations of the taenia coli which dont extend across the whole width of the bowel.
5% of intestinal obstructions show no abnormality on plain X-rays - because bowel is completely distended with fluid in a closed loop and without the fluid levels produced by co-existent gases
TREATMENT
CHRONIC large bowel obstruction slowly progressive and incomplete can be investigated at some leisure (including sigmoidoscopy, colonoscopy and barium enema) and treated electively
ACUTE obstruction of sudden onset, complete and with risk of strangulation, is invariably an urgent problem requiring emergency surgical intervention
PREOPERATIVE PREPARATION IN ACUTE OBSTRUCTION
IV FLUID REPLACEMENT - the large amount of fluid sequestered into into the gut together with losses due to vomiting, means that a lot of fluid may be required
Hartmann's solution or normal saline given with potassium if it's low and renal function satisfactory
if pt shocked plasma expanders may be required
ABX THERAPY - is commenced if intestinal strangulation is likely (or is found at operation)
GASTRIC ASPIRATION - by means of nasogastric suction - helps to decompress the bowel and lessen the risk of inhalation of gastric contents during induction of anaesthesia
OPERATIVE TREATMENT
non-viability is determined by 4 signs:
loss of peristalsis
loss of normal sheen
colour (greenish or black bowel is non-viable; purple bowel may still recover)
loss of arterial pulsation in the supplying mesentery
doubtful bowel may recover after relief of obstruction
should be reassessed and left for few mins wrapped up in a warm wet pack
if extensive bowel is doubtful may reassess in 48hrs via second look laparotomy
GENERAL PRINCIPLE
small bowel in intestinal obstruction can be resected and primary anastomosis performed with safety because of its excellent blood supply
large bowel obstruction is treated by resection of the obstructing lesion with a primary ileocolic anastomosis in the case of lesiosn proximal to splenic flexure
left sided lesions are managed by excision of the affected segment and exteriorising the 2 ends of colon as a temporary colostomy and mucous fistula
if the distal end will not reach the surface, it is closed (Hartmann's procedure)
this difference in management of colonic obstruction reflects the intraluminal bacterial flora and poorer blood supply of the large bowel; a colonic primary anastomosis is perforned, the proximal bowel is first lavaged via a catheter passed through the appendix stump, flushing effluent along colon out via large bore tube in proximal end; a defunctioning loop ileostomy may be performed at the same time to minimise the complications of an anastomotic leak, should one occur.
CONSERVATIVE TREATMENT
by means of IV fluid and NG aspiration (drip and suck) indicated only under the following conditions
when obstruction is one of the repeated episodes due to massive intra-abdominal adhesions, rendering surgery hazardous and when once again a short period of observation with conservatice treatment is indicated
an inc in distension, aggravation of pain, an inc in abdominal tenderness or a rising pulse are indications to abandon conservative treatment and to re-explore the abdomen
when chronic obstruction of the large bowel has occurred. here it is reasonable to attempt to remove the obturating faeces by enema, prepare the bowel and carry out a subsequent elective operation
when distinction from postop paralytic ileus is uncertain and when a period of careful observation is indicated
CLOSED LOOP OBSTRUCTION
characterised by increasing distension of a loop of bowel due to a combination of complete obstruction distally and a valve-like mechanism proximally allowing the bowel to fill but preventing reflux back
it is most commonly seen with a left sided colonic obstruction, in the presence of a competent ileocaecal valve
the caecum, the most distensible part of the large bowel, blows up like a balloon and perforation of the caecum with faecal peritonitis may occur if the obstruction is not rapidly relieved
diagnosis made on x-ray showing characteristic dilatation of the caecum
other eg of closed loop obstruction include volvulus (gastric, caecal, sigmoid) and stomal obstruction of the afferent loop following Polya partial gastrectomy
ADHESIVE OBSTRUCTION
intra-abdo adhesions are an almost invariable consequence of abdo or pelvic surgery - most cases are symptomless, but a small number of pts deelop small bowel obstruction. may occur at any time from immediate postop period to many yrs later - 3/4 of SBO caused by adhesions
large bowel obstruction from this cause is extremely rare
treatment is initially conservative with NG suction and IV fluid replacement - however clinical features of strangulation, peritonitis or failure to respond to conservative regimen are indications for urgent laparotomy
VOLVULUS
DEFINITION
twisting of a loop of bowel around its mesenteric axis which results in a combination of obstruction together with occlusion of the main vessels at the base of the involved mesentery
most commonly, it affects the sigmoid colon, caecum and small intestine but volvulus of the gallbladder and stomach may also occur
AETIOLOGY
precipitating factors include:
abnormally loaded loop as in the sigmoid colon of chronic constipation
a loop fixed at its apex by adhesions around which it rotates
abnormally mobile loop of intestine eg congenital failure of rotation of the small intestine or a particularly long sigmoid loop
a loop of bowel with a narrow mesenteric attachment
SIGMOID VOLVULUS
this occurs usually in elderly, constipated pts. it is 4 times more common in men than women
it is relatively rare in UK
the loop of sigmoid colon usually twists anticlockwise from one half to three turns
CLINICAL FEATURES
sudden onset of colicky pain with characteristic gross and rapid dilatation of the sigmoid loop
a plain x-ray or CT of the abdo shows an enormously dilated oval gas shadow on the left side, which may be looped on itself to give the typical 'bent inner tube' sign
if left untreated, the strangulated bowel undergoes gangrene, resulting in death from peritonitis
the caecum is usuallly visible and dilated in the RLQ, distinguishing it radiologically fom caecal volvulus
TREATMENT
a long soft rectal tube is passed through a sigmoidoscope and advanced into the sigmoid colon, this often untwists an early volvulus and is accompanied by the passage of vast amounts of flatus and liquid faeces
if this method fails,volvulus is untwisted at laparotomy and the bowel is decompressed via a rectal tube
if gangrene has occurred - excise the affected segment and the the 2 open ends are brought out as a double barrelled colostomy and later closed (Paul-Mikulicz procedure)
recurrent sigmoid volvulus is an indication for elecive resection of the redundant sigmoid loop
CAECAL VOLVULUS
usually assoc with a congenital malrotation, the caecum and proximal ascending colon rotate beyond the right iliac fossa during development so that instead of being fixed in the RIF , it has a persistent mesentery
clinically there is an acute onste of pain in the RIF with rapid abdo distension
plain radiograph or CT of the abdomen shows a grossly dilated caecum, which is often ectopically placed and is frequently located in the LUQ of the abdo
TREATMENT
At laparotomy, the volvulus is untwisted. right hemicolectomy is necessary if the caecum is infarcted and it is also the most reliable way to prevent recurrence
SMALL INTESTINE VOLVULUS IN ADULTS
occasionally the apex of the volvulus bears a tumour. in africa, primary volvulus of the small bowel is relatively common and may be due to a loading of a loop of gut with large quantities of veg - clin picture is of acute intestinal obstruction
TREATMENT - early op - simple untwisting and treat underlying cause - if any gangreene = resection
this may occur when a loop of small intestine is fixed at its apex by adhesions or by a fibrous remnant of the vitellointestinal duct (often assoc with a meckel's diverticulum)
MESENTERIC VASCULAR OCCLUSIONS
embolism or thrombosis of the mesenteric vessels = obstruction without occlusion of the bowel
AETIOLOGY
mesenteric embolus
may arise from left atria in AF , a mural thrombus secondary MI, a veg on a heart valve or an atheromatous plaque on aorta
occassionally may be paradoxical embolus originating in the deep leg veins and crossing the septum of the heart through a patent foramen ovale
mesenteric arterial thrombosis
usually thrombosis secondary to atheroma. arterial occlusion may also be secondary to atheroma
arterial occlusion may also be secondary to an aortic dissection
mesenteric venous thrombosis
assoc with portal HTN, or may follow splenectomy for thrombocytopenic purpura, pressure of a tumour on the superior mesenteric vessels or septic thrombophlebitis (eg secondary to Crohn's) Both mesenteric arterial and venous thrombosis are well documented in previously healthy young women on oral contraceptives and are also assoc with thrombophilias such as antithrombin III deficiency
non-occlusive infarction of the intestine
pts with grossly diminished CO and mesenteric BF consequent upon MI or CCF; may also follow cardiopulmonary bypass, particularly in pts with DM
PATHOLOGY
Results in infarction of affected bowel - bleed into gut wall, lumen and peritoneal cavity
gangrene and subsequent perforation of ischaemic bowel occurs
impaired arterial blood flow to gut without infarction may produce intestinal angina - pain follows meals = eat less = weight loss
may be associated steatorrhoea
minor degrees of occlusion may be overcome by collateral circ developed
one or even two of main arteries (coeliac, superior and inferior mesenteric) may be occluded without symptoms
CLINICAL FEATURES
may be some pre-existing factor eg heart lesion or liver disease
TRIAD: acute colicky abdo pain, rectal bleeding, shock in an elderly pt
however, symptoms may be quite mild initially
abdo is generally tender, a vague tender mass may be felt= infarcted bowel
TREATMENT
shock treated by blood transfusion
resect gangrenous bowel but obv impossible when whole SMA supply (small intestine and right side of colon) is affected - usually fatal
revascularisation using a saphenous vein conduit to take blood from iliac artery to SMA may be possible
resection of definitely infarcted bowel and bowel of dubious viability is left and inspected at a subsequent laparotomy following day
young if had extensive resection can have long term parenteral nutrition with intestinal transplant as an alternative
NEONATAL INTESTINAL OBSTRUCTION
continuous vomiting in newborn suggests intracranial injury, infection or obstruction
bile vomiting in neonate indicates intestinal obstruction
in addition to vomit there may be abdo distension and visible peristalsis
plain X-ray of abdo shows distended loops of intestine with fluid levels
INTESTINAL ATRESIA
may be a septum, complete or partial or a complete gap which nay be assoc with a corresponding defect in the mesentery. Multiple segments may be involved
TREAT - resectopm pf tje stricture and anastomosis - mortality high
VOLVULUS NEONATORUM
congenital malrotation of bowel. caecum remains high and midgut mesentery is narrow and drags accross duodenum which may thus also be obstructed
due to narrow attachment of mesentery = readily undergoes volvulus - untreated whole midgut will become gangrenous
TREATMENT - laparotomy ASAP - untwist and widen the mesenteric attachment to retroperitoneum
adhesions between caecum and duodenum are divided and the caecum and ascend colon are placed on left side or midline
MECONIUM ILEUS
80% with this have CF - because of loss of intestinal mucus and blockage of pancreatic ducts with loss of enzymatic digestion, the lower ileum of fetus becomes blocked with inspissated, viscous meconium
perforation of bowel may occur in intrauterine life (meconium peritonitis)
CLINICAL FEATURES - PC acute obstruction in first days of life, gross abdo distension and vomiting. the loop of ileum impacted with meconium may be palpable. xray of abdo shows in addition to distended coils of bowel, the typical mottled ground glass appearance of meconium
TREATMENT - may clear meconium by instillaton of gastrografin per rectum under xray control
if fails or bowel perforates - indicates surgery = enterotomy and removal of the inspissated meconium by lavage
postop infant given pancreatic enzyme supplements by mouth
prognosis depends on extent of chest being affected - lack of mucus secretion of bronchi, recurrent chest infec is inevitable
NECROTIZING ENTEROCOLITIS
seen in premature infants -mesenteric ischaemia - permits bacterial invasion of mucosa
terminal ileum, caecum and distal colon are commonly affected
culmination of disorders: hypoxia, hypotension, hyperviscosity = reduce distal perfusion, together with sepsis and presence of umbilical artery cannula
CLINICAL FEATURES
generalised sepsis, vomiting and listlessness, abdo distended and tense
blood and mucus are passed per rectum in over half cases
affected bowel may perforate or the condition resolve with stricture formation
abdo xray - distended loops of intestine, gas bubbles may be seen in bowel wall and portal vein
pneumoperitoneum signifies intestinal perforation
TREATMENT
resuscitated and comenced on total parenteral nutrition and broad spectrum abx
indications for surgery are failure to respond, profuse intestinal haemorrhage and evidence of perforation or obstruction due to stricture formation
comprises resection of frankly gangrenous or perforated segements of intestine with primary anastomosis when possible to avoid ileostomies
HIRSCHPRUNG'S DISEASE
may present as acute obstruction in neonate 80% male
PATHOLOGY - congenital or aganglionic megacolon is produced by faulty development of the parasympathetic innervation of distal bowel - there is absence of ganglion cells in the submucosal plexus of auerbach and intermyenteric plexus of meissner affecting the rectum which sometimes extends into the lower colon and rarely affecting the while of large bowel
the involved segment is spastic, causing a functional obstruction with gross proximal distension of the colon
suggested to be mutation of RET proto-oncogene
CLINICAL FEATURE- obstructive features commence in first few days of life - failure to pass meconium, death results if untreated
less marked eg = PC constipation in infancy and gross abdo distension and stunted growth
many untreated infants develop severe life threatening enterocolitis within first 3 mths of life
PR reveals narrow empty rectum above which faecal impaction may be felt, this examination is usually followed by a gush of flatus and faeces
SPECIAL IX - abdo xray = dilated gas filled loops of bowel throughout abdo except pelvis
barium enema - narrow rectal segment which the colon is dilated and full of faeces
rectal wall biopsy - absence of ganglion cells
DDX - acquired megacolon, condition of severe constipation at age 1-2 yrs often in a child with mental retardation PR has impacted faeces being present right up to anal verge - normal ganglion cells - relieved by regular enemas and aperients
TREATMENT - if child obstructed in neonatal period = colostomy performed
elective surg when infant 6-9mths old or until at least 3mths have elapsed after a colostomy has been established
the aganglionic segment is resected and an abdominoperineal pull through anastamosis performed between normal colon and anal canal
ANORECTAL ATRESIAS
spectrum of abnormalities from imperforate anus to complete absence of anus and rectum - result from failure of breakdown of the septum between the hindgut and the invaginating ectoderm of the proctodaeum- 50% assoc with fistula
CLINICAL FEATURES
TREAT - if thin septum (<1cm) = divided with suture of edges of the defect to the skin
if extensive gap between the blind end and the anal verge, a colostomy is fashioned with a later attempt at a pull through operation at about 2y/o
if vaginal fistula present - op not urgent as bowel decompresses thru vagina - electie surg when girl is older
if a rectourethral or vesical fistula is present (meconium escaping in the urne) - the fistula must be closed urgently with either colostomy or reconstruction of anus in order to prevent ascending UTI
anus may be entirely absent or represented by a dimple or a blind canal
diagnosis may be suspected on prenatal US
xraying the child held upside down
assoc with vertebral and other congen defects - diagnosis should have US or MRI of spine
INTUSSUSCEPTION
Prolapse pf pme [ortion of the intestine into the lumen of the immediately adjoining bowel
the prolapsing or invaginating bowel is called the intussusception
TERMINOLOGY
ILEOILEAL - ileum is invaginated into the adjacent ileum
ileocolic - an ileoileal intussusception that extends through the ileocaecal valve into the colon, this is the most common sort (75%)
ILEOCAECAL - apex of the intussusception
COLO-COLIC - colon invaginates into an adjacent colon (usually because of a protruding tumour of the bowel wall)
AETIOLOGY
95% Occur in infants or young children in whom there is usually no obv cause
the mesenteric lymph nodes in these pts are inavariably enlarged - lymphoid tissue in peyers patches undergoes hyperplasia because of an adenovirus - protrudes lumen act as foreign body - propelled by peristalsis distally, dragging bowel behind
polyp,carcinoma,intestinal lymphoma or inverted Meckel's diverticulum may form the apex of the intussuscep.
blood supply cut off by direct pressure of outer layer - gangrene if untreated
CLINICAL FEATURES
3-12mths it occurs commonly
boys x2 than girls
screaming, pallor, vomit, passage of blood/slime per rectum = redcurrent jelly
sausage shaped tumour on palpation anywhere except RIF, may also be under costal margi nso not felt
US can confirm diagnosis
if neglected after 24hr abdo becomes distende, faeculent vomiting occurs and child becomes intensely toxic - due to gangrene and assoc peritonitis
TREATMENT IN INFANTS
NON-OPERATIVE
barium is run in per rectum and xray confirmation of diagnosis is established
if intussusception is recent it may be completely reduced hydrostatically by the pressure of the column of barium and this is confirmed radiologically
OPERATIVE
reduced at laparotomy by squeezing its apex backwards out of the contaning bowel
in late cases reduction may be impossible or bowel gangrenous so resection may be necessary
mortality very low in first 24hrs but high in irreducible or gangrenous cases
may recur in small %